2 files changed, 14 insertions, 4 deletions

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index e5996984ddd0..9aaf5bfdad1a 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -242,6 +242,8 @@ size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
  */
 
 #define SG_MITER_ATOMIC         (1 << 0)         /* use kmap_atomic */
+#define SG_MITER_TO_SG          (1 << 1)        /* flush back to phys on unmap */
+#define SG_MITER_FROM_SG        (1 << 2)        /* nop */
 
 struct sg_mapping_iter {
         /* the following three fields can be accessed directly */
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index a295e404e908..0d475d8167bf 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -314,6 +314,7 @@ void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
         miter->__sg = sgl;
         miter->__nents = nents;
         miter->__offset = 0;
+        WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG)));
         miter->__flags = flags;
 }
 EXPORT_SYMBOL(sg_miter_start);
@@ -394,6 +395,9 @@ void sg_miter_stop(struct sg_mapping_iter *miter)
         if (miter->addr) {
                 miter->__offset += miter->consumed;
 
+                if (miter->__flags & SG_MITER_TO_SG)
+                        flush_kernel_dcache_page(miter->page);
+
                 if (miter->__flags & SG_MITER_ATOMIC) {
                         WARN_ON(!irqs_disabled());
                         kunmap_atomic(miter->addr, KM_BIO_SRC_IRQ);
@@ -426,8 +430,14 @@ static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
         unsigned int offset = 0;
         struct sg_mapping_iter miter;
         unsigned long flags;
+        unsigned int sg_flags = SG_MITER_ATOMIC;
+
+        if (to_buffer)
+                sg_flags |= SG_MITER_FROM_SG;
+        else
+                sg_flags |= SG_MITER_TO_SG;
 
-        sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC);
+        sg_miter_start(&miter, sgl, nents, sg_flags);
 
         local_irq_save(flags);
 
@@ -438,10 +448,8 @@ static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
 
                 if (to_buffer)
                         memcpy(buf + offset, miter.addr, len);
-                else {
+                else
                         memcpy(miter.addr, buf + offset, len);
-                        flush_kernel_dcache_page(miter.page);
-                }
 
                 offset += len;
         }